1. Field of the Invention
The invention relates to a vision aid, and more particularly to an artificial retinal system and a retinal implant chip.
2. Description of the Related Art
Retinitis Pigmentosa (RP) and age-related macular degeneration (AMD) are two diseases resulting from degeneration of photoreceptors of the retina. AMD is the main cause of adult blindness in western countries. No effective treatment is available for the blindness caused by these diseases. However, an artificial retina which can replace the photoreceptors has been employed to restore vision. Conventional artificial retina includes a solar cell for receiving and converting an optical image into current to stimulate the remaining ganglion cells, such that visions of patients blinded as a result of degeneration of photoreceptors can be restored. In the prior art, insufficient power supply of the solar cell is an issue, and use of wiring and routing for providing power arises in safety concerns.
In U.S. Pat. No. 7,622,702, a divisional power supply scheme (DPSS) is disclosed to increase the output current from an image sensing pixel array. The image sensing pixel array includes a plurality of solar cells, and is divided into N blocks. Only one block is activated at a time and the blocks are activated in turns. As long as the activation frequency is over the desired frequency of persistence of vision (about 30 Hz), the patient can have a normal vision. In this scheme, assuming the current provided by the solar cell is ISC, the current obtained by the activated block is ISC. If all the N blocks can be activated at the same time, current obtained by each block is ISC/N. Thus, the DPSS can increase several times the output current.
However, image projected to the image sensing pixel array may have bright and dark parts. If the image is used as both an image signal and the sole power source in the DPSS, the photocurrent generated from the dark parts shall be smaller than that generated from the bright parts. This is normal for image sensing to maintain a contrast of the image. As a solar cell, however, the lower illumination generates smaller photocurrent and smaller power, thereby resulting in unstable power supply.
US patent application publication no. US20050090875 discloses a display and projector to be worn on a head of the patient for providing sufficient light into the eyeballs, so as to increase the output current from the solar cell. The proposed scheme, however, results in lower image contrast.